for a quick reference it is the same height and thickness as a 15c but .088" or 2.2mm longer. The keys are .06" or 1.5mm closer to the sides, the key spacing is .01" or .25mm closer together and we have one extra row of keys.

Feel free to comment on where various keys should go and what other functions should go on the extra keys. Please note the INV key that is there so there is no need to label the inverse for SIN, COS, TAN . . . functions, that way you also clear up space on the keyboard where those functions would be for other blue g shift key functions.

It might offend the purists (moving the "INV" function away from its (almost) current location, but it seems to me that it should be placed next to (to the left of, for those of us right-handed folks who dominate the world) the SIN, COS, TAN buttons (and very close as well to the other INVertable operations (i.e. 10^x, e^x, etc.)) What happens if you push INV before the wrong button (i.e. something that doesn't have an inverse operation)? I guess you should get an error message.

It might look impressive, but do you really need all those digits for display? As has been mentioned here recently, do you ever need 10+ digits of precision? Perhaps when taking differences between comparable sized numbers. (I occasionally deal with very precise timing - picosecond precision for millisecond intervals, but that gets done in the computer with double or even quadruple precision.)

I'm glad you asked that. There are 43 keys on that design. If you subtract the ENTER, ON, f, g, INV, and an ALPHA key that leaves 37 keys. If you also omit the numeric keys, which many would want to not be part of the alpha shifted set, that leaves you with 27. That is enough, but I really don't think I like the idea. I am thinking this should be more of a basic scientific calculator, in the tradition of the 10C series. I added the second line on the display because it would fit with out moving any keys. While I don't think the second line really makes RPN easier to use, I do think it makes it easier to learn. Personally I also have a little bit more of a "warm fuzzy feeling" if I can see both numbers I am about to act on and I think it gives you one more chance to notice a potential error in your previous result. The INV key wasn't my idea. I read about it in the comp.sys.hp48 forum, and I thought it sounded like a great way to keep keyboard clutter down and get more functions on the keyboard.

Some of the other things I would change from the 15C are, speed and memory those are no brainers. I would keep the 20 directly addressable memory registers exactly the way they are, but I would change the stats functions so they stored their data in their own dedicated registers (we can easily have enough memory for that on a simple scientific calculator today). You may have noticed that PI has it's own key, I really like that. Other than that I don't see where I would change much else on the 15C I just added the extra buttons to allow for more functions that other people might like to see. Maybe add the most common financial functions of the 12C, so all the engineers that switch over to the "dark side" can do all the TVM stuff with their scientific calculator.

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It might look impressive, but do you really need all those digits for display? As has been mentioned here recently, do you ever need 10+ digits of precision?

I'm glad you asked. Actually I was the one that mentioned that more than 10 digit precision isn't necessary. So why the 16 digits? Well I thought you could use it to show both the real and imaginary parts of a complex number on one line. Or if you wanted to display more precision than that you could use both lines to display a complex number. I was also thinking you could do something similar with 2D vectors. Have a vector mode that worked very close to the way the complex mode works on the 15C.

Maybe we could use the extra room on the keyboard provided by the INV key and extra keys to add the functions that the 16C had? Maybe role up the 15C, 16C and 12C in to one calculator. Maybe as OpenRPN suggested we could have a small overlay for 4 user buttons and it could come standard with a CS and Financial overlay.

hp 33s display is great (once you fix the decimal point size).
16 places (including sign place) is enough for sixteen hex digits.
It is also enough for sign+15 digits of internal accuracy shown using SHOW to view mantissa only.
You can used for sign+mantissa+[E/small E&sign]+exponent, eg: 1+10+1+3=15.
Two lines will show X&Y or a complex pair or (setting a flag) X&Y using "compressed" complex pair with reduced number of digits shown
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Combining the 12+15+16 = 43 would be best idea since sliced bread, gun powder and compass combined.
The 16C top row of keys A..F should be different in the financial mode.
Maybe we simply need one more row of keys and put them slightly closer each other.
I recommend that a second press on any of the three shift keys would invoke the inverse (or special chars).
Three shift keys are needed of which one is ALPHA to use the equation editor.
I simply want a better 33s, which is 43s and it will be more like 12+15+16 combined, except that the LCD will be full dot matrix for A..Z labels and "textual" programming eg. no more keycodes.
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